Internal combustion engines generate exhaust as a by-product of fuel combustion within the engines. Engine exhaust contains, among other things, un-burnt fuel, particulate matter such as soot, and harmful gases such as carbon monoxide or nitrous oxide. To comply with regulatory emissions control requirements, it is desirable to reduce the amount of soot and harmful gases generated by the engine. Due to the rising cost of liquid fuel (e.g. diesel fuel) and to comply with the emissions control requirements, engine manufacturers have developed dual-fuel engines. Using a lower-cost fuel together with liquid fuel helps improve the cost efficiency of the engine. Further, combustion of the gaseous fuel and liquid fuel mixture lowers the production of undesirable emissions from the engine.
In an exemplary dual-fuel engine, the gaseous fuel may be introduced into combustion chambers of the engine during an intake stroke. Because exhaust valves of the combustion chambers may remain open for a portion of the intake stroke, some of the gaseous fuel can escape or “slip” out through the open exhaust valves. The fuel that escapes from the combustion chambers does not participate in combustion, reducing the efficiency of the engine. Additionally, the escaping un-burnt gaseous fuel contributes to the total amount of undesirable emissions produced by the engine.
One technique for reducing gaseous fuel slip from the combustion chambers is disclosed in International Publication No. WO 2013/0686640 to Häglund (“the '640 publication”) that published on May 16, 2013. The '640 publication discloses various embodiments to remove and treat un-burnt gaseous fuel trapped in dead volumes in the combustion chamber where no combustion occurs. The '640 publication discloses an arrangement of conduits that removes a portion of the exhaust containing the un-burnt gaseous fuel separately from the remaining portion of the exhaust. The '640 publication also discloses a processing unit for treating the portion of the exhaust containing the un-burnt gaseous fuel. The treated exhaust is then allowed to mix with the remainder of the exhaust.
Although the '640 publication discloses the use of a processing unit to treat un-burnt gaseous fuel for improving engine emissions, the disclosed apparatus and method may still not be optimal. In particular, the disclosed apparatus of the '640 publication removes the un-burnt gaseous fuel after completion of combustion in the engine cylinders. Thus the un-burnt gaseous fuel does not contribute to generation of power in the engine, reducing the efficiency of the engine. Further, the disclosed apparatus of the '640 publication requires the use of additional ducting and the use of a processing unit, which may increase the cost of manufacturing and operating the engine.
The engine system of the present disclosure solves one or more of the problems set forth above and/or other problems in the art.